The invention relates to an aramid yarn provided with a superabsorbent material. The invention further relates to a process for manufacturing such a yarn. This type of yarn can be utilized in cables, more particularly in optical communications cables, in this way functioning simultaneously as a reinforcing member and as a water blocking agent.
An aramid yarn provided with a superabsorbent material and the manufacture of such a yarn are known from European Patent Publication No. 351,100. According to this publication Kevlar.RTM. aramid, a commercially available yarn of poly(p-phenylene terephthalamide) from E. I. DuPont de Nemours, was impregnated with a superabsorbent material. After being impregnated, the treated yarn was dried, so that a film was formed in and around the yarn's interstices. In one embodiment of this treatment method, the yarn was impregnated with a superabsorbent material derived from an aqueous solution comprising acrylate polymeric material which combines acrylic acid and sodium acrylate functionalities and water. The resulting product was used as a reinforcing material for the manufacture of a communications cable with water blocking properties.
International Wire & Cable Symposium Proceedings 1988, pp. 307-308, describes a Kevlar.RTM. aramid yarn treated with water swellable polymers. Such a yarn was used as a reinforcing material in optical cables, providing them with water blocking properties. This publication discloses neither the composition of the water swellable polymer, nor the manner in which treatment of the yarn with this polymer was carried out.
Also, it is known that cables can be provided with a superabsorbent polymeric material by being contacted with such a material in powdered form, optionally with use being made of electrostatic forces.
There are, however, various drawbacks to each of the above-mentioned methods of applying a superabsorbent material to a cable or yarn surface. A drawback to impregnating an aramid yarn with a superabsorbent material dispersed in an aqueous system is that, due to the superabsorbent material's high viscosity-enhancing action, uniform feeding of it is extremely difficult, if not impossible. Further, on account of the limited concentration of superabsorbent material in the impregnating liquid only a small quantity of it can be applied to the yarn during each treatment. Another drawback to this method is that the comparatively large amount of impregnating liquid which is applied to the yarn with the superabsorbent material needs to be removed by evaporation.
A disadvantage to handling superabsorbent materials in powdered form is that special equipment is required and that, furthermore, it is hard to distribute the powdered material uniformly over the yarn. An additional drawback to handling powders is that dust can be raised, with the attendant risk of explosions and health hazards.
U.S. Pat. No. 4,888,238 discloses a method of preparing superabsorbent synthetic fibers coated with a water absorbent polymer. This patent mentions the use of various synthetic fibers including polyester, polyolefin, polyacrylonitrile, polyamide, rayon, cellulose acetate, Dacron polyester, nylon and bicomponent fibers. The fibers are added to an aqueous solution of an anionic polyelectrolyte, a polyvalent metal salt and a neutralizing agent. They are then fluff dried to evaporate the neutralizing agent and to form a complex of the polyelectrolyte in situ as a coating thereon. Among the drawbacks to this method are that such a method can only be applied to short fibers, the evaporating neutralizing agent, i.e. ammonia, pollutes the atmosphere, and the coating of the superabsorbent is resolubilized at a pH above 7.